[RFC PATCH 4/6] svcrdma: preserve rq_next_page in svc_rdma_save_io_pages

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

svc_rdma_save_io_pages() transfers response pages to the send
context and sets those slots to NULL. It then resets rq_next_page
to equal rq_respages, hiding the NULL region from
svc_rqst_release_pages().

Now that svc_rqst_release_pages() handles NULL entries, this
reset is no longer necessary. Removing it preserves the
invariant that the range [rq_respages, rq_next_page) accurately
describes how many response pages were consumed, enabling a
subsequent optimization in svc_alloc_arg() that refills only
the consumed range.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/svc_rdma_sendto.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index 914cd263c2f1..17c8429da9d5 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -858,7 +858,8 @@ int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma,
 
 /* The svc_rqst and all resources it owns are released as soon as
  * svc_rdma_sendto returns. Transfer pages under I/O to the ctxt
- * so they are released by the Send completion handler.
+ * so they are released only after Send completion, and not by
+ * svc_rqst_release_pages().
  */
 static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
 				   struct svc_rdma_send_ctxt *ctxt)
@@ -870,9 +871,6 @@ static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
 		ctxt->sc_pages[i] = rqstp->rq_respages[i];
 		rqstp->rq_respages[i] = NULL;
 	}
-
-	/* Prevent svc_xprt_release from releasing pages in rq_pages */
-	rqstp->rq_next_page = rqstp->rq_respages;
 }
 
 /* Prepare the portion of the RPC Reply that will be transmitted
-- 
2.53.0